Digitally controlled bandwidth sampling filter-detector
AssigneeMotorola, Inc.
InventorRobert M. Bennett
Life of this patent
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Abstract
An improved sampling filter detector circuit for sampling input signals of different frequencies and providing a detect signal when the input frequency has a desired predetermined value. The circuit is suitable for use as a tone detector for continuous tone control squelch systems. The sampling filter detector substantially eliminates response to low order harmonics of the desired frequency and provides the ability to program the filter detector bandwidth by digital means without altering passive components thereby permitting reverse burst detection.
Claims10
An improved sampling filter for processing an input signal applied to an input terminal to detect at least one desired tone of a plurality of tones, comprising:
- (a) a resistor, coupled to the input terminal;
- (b) a plurality of switch means, coupled to the resistor, each switch means including an output and a control input;
- (c) an individual capacitor coupled to the output of each switch means and each capacitor coupled to a reference voltage;
- (d) control means, coupled to the switch means control inputs, for activating each switch means for a switching period equal to approximately one-half the period of the desired tone, said control means including means for successively opening and closing said switching means at a frequency higher than the product of the frequency of the desired tone multiplied by said plurality of switch means, and so that at least two switches overlap in operation but no more than one switch is closed at any time;
- (e) a peak voltage follower having inputs and an output, an input of which is coupled to each of the capacitors;
- (f) a valley voltage follower having inputs and an output, an input of which is coupled to each of the capacitors;
- (g) comparator means, coupled to the output of the peak follower and the output of the valley follower for providing a detector output when one of the outputs of said peak and valley follower exceeds the other.
Dependencies are inferred from the claim text.